This invention relates generally to vibration sensing and more specifically to a vibration sensing device that detects displacement of an object and provides information about the direction and speed of the displacement.
Most vibration sensing devices are of a strain gauge type or piezoelectric devices. Strain gauge type vibration sensors employ an electrical resistance that varies with the magnitude of a vibration and converts an electrical resistance change to a corresponding analog voltage output to produce a vibration detection signal. Similarly, piezoelectric devices employ quartz crystals that convert induced strain to a corresponding analog voltage output. In both types of vibration sensing devices, the changes in the electrical resistance or piezoelectric response provided by the device, in response to the vibrations, are extremely small and complicated circuitry must be provided for filtering noise.
Other methods of detecting vibrations, such as an out-of-balance (OOB) condition of a washing machine, include electronic OOB switches and fluidic pressure switches that can indicate that an OOB condition exists and, in some cases, deactivate the motor of the washing machine when a switch is triggered. An electronic OOB switch is positioned so that the switch is mechanically tripped when a washing machine tub deviates from its normal rotational position within a cabinet. A drawback of this type of switch is that a single deviation of the tub, unrelated to a true out of balance condition and that is unlikely to cause damage, is often sufficient to trip the switch. When the tub is accelerating to a maximum spin speed, for example, it is common to encounter certain natural mechanical frequencies that can induce brief or momentary deviations of the tub sufficient to trip the switch and interrupt the cycle, thereby lengthening the washing time unnecessarily.
Fluidic pressure switches are fairly complex, employing pneumatic generating units to generate a predetermined fluidic pressure in response to deviations of the washing machine tub during the spin cycle. An actuator, which actuator is fluidly coupled to the generating units, provides an actuating position corresponding to an OOB condition. A switch, which is responsive to the actuator in an actuating position, signals that an OOB condition exists.
Existing vibration sensing devices tend to have complex mechanisms or electrical circuitry. Further, current vibration sensing devices generally provide a signal that indicates only that a vibratory or OOB condition exists. Hence, a simple low cost device that not only detects vibration but provides information about the speed and direction of the vibration and which is adaptable to a variety of situations is desirable.
Accordingly, there is a need in the art for an improved vibration sensing device.